Pollination timing effects on kernel set and silk receptivity in four maize hybrids

Silk receptivity and kernel set vary with time of pollination and environment. Our objectives were to evaluate differences in kernel set, silk elongation patterns, and duration of silk receptivity for four hybrids. These experiments used pollen-saturating hand pollinations of four field-grown maize (Zea mays L.) hybrids at varying days after first silk (DAFS) appearance in 1992, 1993, and 1994. Kernel set on primary ears was determined for B73 x MO17 (low silk turgor), WF9 x A632 (high silk turgur), Pioneer 3343, and Pioneer 3379 (Pioneer Hi-Bred Int., Inc., Johnston, IA). WF9 x A632 had the fastest initial silk growth rate, resulting in earlier successful pollination of midbase floret positions. However, these floret positions declined in kernel set at later DAFS due to loss in silk receptivity and poor silk health. Thus, it had a lower final kernel number and a faster decline in kernel set when pollinated 10 DAFS in 1992 and 8 DAFS in 1993 and 1994. Hybrid WF9 x A632 had the lowest receptive trichome surface area, trichome density, and trichome number on its exposed silk surface 3 DAFS compared with the other three hybrids. Hybrid silk trichome length varied and was longer near the silk tip. Although silk elongation patterns were different, silk growth rates for all four hybrids gradually declined to near zero by 8 to 10 DAFS in 1992. We conclude that kernel set and yield stability are impacted by variation among hybrids for silk elongation and senescence.